Forum developed GR-R WAW speaker

Yes of coarse when the drivers play out or in at the same time you'll get changes in pressure. But the amount of mechanical vibration that is canceled is impressive. Normal speakers built with average boxes you can feel a lot of vibration. The transfer of energy into the box through the mounting is very high. Linkwitz did a page on it somewhere. For those not using hardwoods or really thick plywood it's a great way to keep the cost of the box reasonible while greatly reducing vibrations. Compared to 3/4mdf in a non bipole the reduction is very impressive. (on 3/4mdf in for example a bookshelf you can really feel a lot of vibration)

What I've been wanting to do is make a capable speaker that is a FAST, Fullrange assisted sub tech. Maybe that's the right acronym, I'm not even sure! The point is to use a fullrange driver with a bass driver.

There is a movement to get people to start using WAW (Woofer Assisted Wideband) instead of FAST which is almost universally disliked.

The concept that you are proposing is very workable and exactly s we have done with Tysen V2.

This specific implementaion uses the Fostex FF85wk and a pair of Silver Flute W14. The push-push loading of the bass drivers goes a long way to reducing box-load and dramatically reduces the possibity of exciting potential box resonances.

The proximity of the drivers allows one to keep the XO above the 1/4 wavelength of the centre-to-centre distance. We do this with the typically 250 Hz PLLXO (also works with the 4th order XOs in my partners Onkyo HT receiver). A passive XO was also developed, it turned out to be about 450 Hz. From these XO points one may find that typical plate-amps do not have the range to XO high enuff. Use of a larger midTweeter might allow for that to work, the quality of the XO in the plate amp maybe a limiting factor.

The push-push loading of the bass drivers goes a long way to reducing box-load and dramatically reduces the possibity of exciting potential box resonances.

I am not sure why you guys think that this mounting reduces box load. The load the box sees is exactly the same no matter where the woofers are mounted. Box resonances or the potential for box resonances remain unchanged.

If you want to control box resonances then brace it well and add No Rez. Problem solved.

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A passive XO was also developed, it turned out to be about 450 Hz.

That's well up into the heart of the mid-range. that's not a good place for a phase shift of chopping up the vocal region into dis-similar drivers.

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From these XO points one may find that typical plate-amps do not have the range to XO high enuff. Use of a larger midTweeter might allow for that to work, the quality of the XO in the plate amp maybe a limiting factor.

The plate amps are not a problem if crossing below 200Hz. The size of passive crossover parts for the low crossover point are more of an issue if the order of the crossover gets high. Really large cap values or iron core inductors are much more harmful.

The biploars I have played with have minimal vibration. My X-LS is the exact recommended box w/ bracing and no-rez still vibrate a lot. In these cases it is just my finger accelerometer judging, but it is very easy to tell. The M165 is more of a beast than people give it credit for, I's say.

I cannot speak for what bipoler setups you have tried Danny. And who said anything about not using bracing?

450hz isn't "ideal" but 2khz~ for tweeters isnt either, we do it anyway.

I am not sure why you guys think that this mounting reduces box load. The load the box sees is exactly the same no matter where the woofers are mounted. Box resonances or the potential for box resonances remain unchanged.

You make the assumption here that most of the energy that can excite box resonances comes from the changes in air pressure inside the box. It is very easy to show that this is not the case and much more energy comes from the direct connection of the driver basket to the box. Push-push done properly kills some (guess) 90% of the driver vibration thru active cancelation, and even more so at the lower frequencies that are more likely to excite the box in a negative manner..

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If you want to control box resonances then brace it well and add No Rez.

It is still necessary to properly brace the box. And as to NoRez i have not had positive results using it.

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That's well up into the heart of the mid-range. that's not a good place for a phase shift of chopping up the vocal region into dis-similar drivers.

There are compromises involved no matter where you XO. A lower XO is advantageous in that it keeps more of the music in the FR/midTweeter. Cross a bit higher and you can play louder. That is of particular importance with a small 3” FR used as midTweeter.

It is important that the helper driver has very good HF extension, the SF W14 reach up to something like 5k on-axis, the Alpair 12pw and Peerless 830870 we use in some other applications reach 10k, the other midbass we have used only goes to 1.5k but that speaker is also on a wide baffle and we have pushed the XO down to 160-180 Hz.

All of these designs were executed with an eye towards 1st order PLLXO, and that coupled with less than 1/4 wl XO point makes a phase coherent result easy.

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The plate amps are not a problem if crossing below 200Hz. The size of passive crossover parts for the low crossover point are more of an issue if the order of the crossover gets high. Really large cap values or iron core inductors are much more harmful.

I have not yet tried every plate amp on the planet but of the many i have, the amps are of 2nd rate execution and the XOs not of the type we’d be inclined to use and usually only reach up to about 150 Hz.

I am a firm believer that an XO at about 200 Hz or lower is much better done actively, and all of our WAW have been designed with an eye to that. The passive XOs were designed to give a complete set of options for anyone purchasing a paid planset subscription.

You make the assumption here that most of the energy that can excite box resonances comes from the changes in air pressure inside the box.

No, I am saying that the alignment you are using doesn't change that aspect.

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It is very easy to show that this is not the case and much more energy comes from the direct connection of the driver basket to the box.

Oh, I am well aware of what can be transmitted from the driver frame to the baffle. This is why we use polymer frames on all of our drivers. And the difference between our polymer frames and some metal frames can be fairly significant.

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Push-push done properly kills some (guess) 90% of the driver vibration thru active cancelation, and even more so at the lower frequencies that are more likely to excite the box in a negative manner..

It can kill some of the overall force placed on the box, but it will have little to no effect on the baffle that each driver is mounted to. The vibration that the driver causes on the baffle is still present. You are just causing an out of phase vibration on the opposite panel to cancel it. That can have a positive effect. But there are easier and more effective ways to handle cabinet wall vibration.

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And as to NoRez i have not had positive results using it.

I have never heard of anyone not having positive results with it. It is known to be quite effective. When did you order some?

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I am a firm believer that an XO at about 200 Hz or lower is much better done actively, and all of our WAW have been designed with an eye to that.

It can kill some of the overall force placed on the box, but it will have little to no effect on the baffle that each driver is mounted to. The vibration that the driver causes on the baffle is still present. You are just causing an out of phase vibration on the opposite panel to cancel it. That can have a positive effect. But there are easier and more effective ways to handle cabinet wall vibration.

If you execute this properly the drivers are physically connected other than just thru the baffle. Vibrations are instantly cancelled by one driver working actively against the other. Differences can be quite dramatic. Enuff that i would not bother with a single driver subwoofer any more… and subsequently being able to get away with 15mm plywood for sub boxes.

this proves to be pretty good:

But one could take it to the next level by replacing the mounting screws with threaded rod that couples the basket bezels together.

The front and back panel get another 3/4" layer making them 1.5" thick solid MDF.

Then the back panel gets a through hole cut out for the servo amp. So the front and back panel aren't much of a panel at all. They are just a frame that supports the woofer or the amplifier. So there is nothing there to resonant.

It seems to me that the more dense the material the better. mdf certainly fits that bill. I suppose the reason for plywood bracing is it's more stiff which I think would make a better brace.

I do like the idea of connecting the two drivers together, if they are locked together they make a very strong brace across the box. It seems to me they would need to be physically connected though so they can't move at all. Otherwise they could still vibrate some.

Of course if you are building a double box full of sand it's probably a mute point.

I like using material of one density for the main box build (say, MDF), and of another density for bracing (say, oak), and then using something like Norez which has a different density entirely. These 3 things together get you close to a "constrained layer damping" effect. The idea is that if you use the same material throughout, then the material itself will have a common resonating point. By using materials of different densities, the resonances are spaced out and are less likely to overlap. Another way to do something similar is to use MDF bonded to a higher density wood like Baltic Birch. Brace it with oak, line it with Norez, I don't think there'd be a less resonant enclosure possible (outside of exotic materials).

The idea is that if you use the same material throughout, then the material itself will have a common resonating point.

That is easily dealt with in the design process. Potential resonance modes can be shifted around by just changing a dimension (ie placement of a brace). And in a subwoofer, the goal is simple, to raise any potential resonances above the bandwidth of the device so that they can never be excited. That requires stiffness as a foremost property.

If 2 materials have the same stiffness the lighter one will have a higher frequency resonance potential. I can/have built subwoofers with 15mm ply and push-push drivers that do not have any resonance until the amplifier is well into clipping and it is WAY louder than it would ever be used… why go to more effort & expense to build something that may (or may not) work as well?

That is easily dealt with in the design process. Potential resonance modes can be shifted around by just changing a dimension (ie placement of a brace). And in a subwoofer, the goal is simple, to raise any potential resonances above the bandwidth of the device so that they can never be excited. That requires stiffness as a foremost property.

If 2 materials have the same stiffness the lighter one will have a higher frequency resonance potential. I can/have built subwoofers with 15mm ply and push-push drivers that do not have any resonance until the amplifier is well into clipping and it is WAY louder than it would ever be used… why go to more effort & expense to build something that may (or may not) work as well?

dave

Because this is a DIY area and we're not really concerned about the feasibility of a design from the standpoint of producing multiples - we're free to try out different things that might (will) work better, even if it takes more time or a little more effort.

I'd also point out that most here know that bracing location will absolutely affect panel resonance. We're ALREADY going to do things like that. The discussion (IMO) is really around "what other things can we do that will give us even better results". IME, using a multi-material approach to cabinet construction can do that.